                1. For batteries to be used for applications such as vehicle starter, electric bikes, electric motorcycles, electric or hybrid vehicles, etc, high voltage is essential owing to the increase of efficiency and the decrease of cost. The increase of voltage requires batteries to be connected in series.        2. Problems associated with batteries in series are:                    a. when one battery has a lower capacity, the capacity of the overall set of batteries is dictated by the capacity of the battery of lower capacity;            b. if the battery possessing the lower capacity can not be charged to full capacity during charging, the performance of the entire battery set will be degraded owing to the lower capacity battery. This is known in the art as cell imbalance;            c. the lower capacity of one specific battery can be caused by either high self discharge or defects during battery production.                        3. Conventional ways to solve the cell imbalance problem are:                    a. sorting the batteries in order to avoid inconsistency of the batteries to be connected in series;            b. charging the batteries separately (e.g. U.S. Pat. No. 6,586,909), in order to overcome the problems mentioned above, however, low voltage is required for charging each battery to full (for example, the lithium iron battery is charged to 3.65V) and this low voltage charging is not energy efficient owing to conversions from normal high voltage AC power source to low voltage DC power.Most prior art systems and methods utilized in making the batteries balanced during charging use complicated circuitry to detect and balance the uncharged batteries (e.g. U.S. Pat. No. 7,068,011, U.S. Pat. No. 7,061,207, U.S. Pat. No. 6,882,129, U.S. Pat. No. 6,841,971, U.S. Pat. No. 6,825,638, U.S. Pat. No. 6,801,014, U.S. Pat. No. 6,784,638, U.S. Pat. No. 6,777,908, U.S. Pat. No. 6,700,350, U.S. Pat. No. 6,642,693, U.S. Pat. No. 6,586,909, U.S. Pat. No. 6,511,764, U.S. Pat. No. 6,271,645).                        